I'd like to welcome you here to the Forum and understand the feelings you are having. Having the original pain in your neck would have made life very hard and limited what you were able to do. I'm glad you have been to see your GP, a neurologist and had several MRIs.
I do not know of a link between neck manipulation and proven incidence of stoke however I'm no doctor. I do think that if you have been examined by a GP, a neurologist and had MRIs then I personally would expect them to find stroke threatening damage of some sort if it was there.
True the cracking sensation in your neck is unexplained, however I guess that may well reduce in time. Again the MRIs would be expected to pick up serious abnormalities.
I know none of this seems like much of a comfort, however ruining your life wiht anxiety over what might happen with your health is no way to live. As you say yourself in your second post it is reducing your ability to study, and this in itself gives extra stress.
May I suggest a couple of things? Firstly to get in touch with uni disability services and talk to them about how illness is affecting your work. They may be able to take this into account, reduce your study schedule without penalty and offer further advice.
Secondly go back to you doctor and psychologist and say that the current regimen is not working and your thoughts are overtaken by fear of stroke and the sensation in your neck and you need your treatment to be reviewed as a result. It may be you are not being treated for the full range of symptoms and things need adjusting. While meditating, exercise and healthy eating, as suggested by your GP, are certainly worth doing perhaps they are not sufficient by themselves.
Anxiety, as I know myself, makes one find it very hard to accept that negative tests are correct. I've had great difficulty in accepting pains in head. chest and abdomen have been caused by anxiety, and at first simply thought the tests were limited or improperly conducted. Over time however I have come to realize they were correct and it is the anxiety which is to blame. Perhaps you are having the same sort of troubles in believing those MRIs and neurological examinations.
It is neither stupid nor a waste of time to try to get help when in your situation, it is simply the sensible thing to do. Trying to deal with this in isolation makes matters harder. Is your dad and other family members or friends there for you?
You are welcome to talk here anytime